Displaying text in OpenGL. why so hard?

Graphics and GPU Programming Programming OpenGL

Started by FantasyVI December 01, 2011 06:33 PM

1 comment, last by Cornstalks 12 years, 4 months ago

105

Author

December 01, 2011 06:33 PM

Hello everyone
so a month ago i started learning OpenGL and not till today that i had to display some text in OpenGL and to my surprise its hard !!
why is it so hard to display text in OpenGL ? why couldn't it be as simple as ( std::cout<<"Text"; ) ?
i did my research i found a lot of way to display text but I'm not sure which one to use. i found bitmap text - texture text - draw text as lines or just use freetype which i found very hard to understand for some reason.
which one should i use? i read somewhere that bitmap text is slow and send a lot of data to the GPU which slows things down. I just want to load fonts change text color and display simple text. nothing fancy i don't want the text to rotate or display it in 3D just old fashion 2D text.

also how can you display text like in old RPG's ? for example display each letter at a time.

also i used SFML and the way they handle text is very nice and clean as far as i know and i think they use freetype library to do so.

Nanoha

2,682

December 01, 2011 06:51 PM

Displaying text is indeed quite hard with OpenGL. I wouldn't use lines, I'd either go for the texture (you put all letters on a image and draw bits of it around the place) or Freetype. I've not tried freetype, it may be hard to understand but the texture bit is alot of work. A long time ago I used this: http://students.cs.byu.edu/~bfish/glfont.php it worked well. Its the texture type implementation.

Displaying text slowly like you have shouldn't be too difficult. You have 2 strings, one is the text in its entirety, the other is the part your actually showing. Every so often (miliseconds/ticks, whatever time your game uses) you add a little more to the displayed text (substring).

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Cornstalks

7,033

December 01, 2011 06:52 PM

why is it so hard to display text in OpenGL ? why couldn't it be as simple as ( std::cout<<"Text"; ) ?

It's hard because that doesn't answer all the questions the graphics library would have: where to draw the text? What size? What color? What rotation? Any kind of special effects, like gradients, transforms, etc? What font? Those are just the beginning questions.

Personally, I used Freetype and I really liked it. It's a little bit difficult to get it set up your first time, but once you've got it working you can just write a wrapper class and use it pretty easily. When I did it I used Freetype to generate the images for each character I'd be using in the game (A-z, 0-9, all the punctuation characters, etc) and then used this to pack the images into a single texture. Then when rendering text, I just drew quads that used only a portion of the font-texture (note that using different font sizes required me to generate a new font-texture (that is, if I wanted it to be pixel perfect, otherwise you can get away without it)).

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Displaying text in OpenGL. why so hard?

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Displaying text in OpenGL. why so hard?

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